Passive Infra-Red

A PIR is wholly enclosed in one part. It consists of a passive IR receiver that measures ambient temperature. If this temperature changes rapidly, like when a person walks across its field of view, an alarm condition is sent to the controller. Outdoor PIR are weatherproof and their lenses can accommodate the harsh ultraviolet rays of the sun. Like the beams they usually have more than one detector, both must trigger simultaneously, to avoid false alarms.